Storage tube



L. PENsAK STORAGE TUBE sept. 1o, ,1957

Filed Aug. 19, 1953 f INVENTOR ../aa/.f Pin/.wx

the stored information.

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States liatent O STORAGE TUBE Louis Pensak, Princeton, N. J., assigner, by mesne assign ments, to the United States of America as represented by the Secretary of the Army Application August 19, 1953, Serial No. 375,246

1 Claim. (Cl. 315-12) This invention is directed to a viewing tube, and more particularly to a charge storage device having a iluorescent screen to provide a visual display of information.

There is a class of electron discharge tubes, described completely in a copending application of M. Knoll, Serial No. 295,768, filed June 26, 1952 and assigned to the same assigneeas the present invention, which utilize a fine mesh screen upon which can be established a pattern of charges corresponding to information to be reproduced for visual inspection. Within the tube a source of electron emission provides an electron discharge directed through the storage screen. On the opposite side of the screen there is mounted a fluorescent screen to receive the electron discharge and to provide a visual display thereof. The storage screen controls the amount of the electron discharge passing through it from point to point, so thatthe luminescent display provided by the fluorescent screen is varied from point to point, in accordance with the charge pattern on the storage screen. Thepattern on the storage screen may be established by either a photocathode providing an electron image discharge or by an electron gun, whose beam is modulated in accordance with incoming signals, while the beam is being scanned over the surface of the storage screen. Such storage viewing tubes provide a greater intensified visual display than is possible with a single modulated electron beam.

However, prior to the time of this invention it has been diiicult to provide bright displays on the iluorescent screen of the stored information in tubes as described above. Furthermore, it has been impossible to selectively erase any desired part of the stored picture at will.

It is therefore an object of this invention to provide an improved charge control storage tube.

Itis another object of this invention to provide a charge control storage tube in which the brightness of the visual picture is greatly improved.

It is a further object of this invention to provide an improved charge control storage tube including means for selectively erasing any part of the stored picture at will.

These and other objects are accomplished in accordance with this invention by providing a charge controlled storage tube including a viewing electron. gun and a writing electron gun. Arranged in operative spaced relationship with the two electron guns is an insulating storage surface and a uorescent screen. Surrounding the envelope adjacent the storage surface is a solenoid. Due to the magnetic field from the solenoid, the electrons from both the writing gun and the viewing gun go through, or land upon, the storage surface perpendicularly tothe plane of the storage surface. Since both the writing beam and the viewing beam are thus collimated the writing beam may be utilized for erasing a selected portion of The present invention will be better understood by referring to the following specification when read in connection with vthe accompanying drawings and in which:

Fig. 1 is a sectional View of a charge controlled storage tube in accordance with this invention; and

Figs. 2 and 3 are graphical representations of conditions existing during operation of the tube of Figure 1.

Fig. 1 discloses a charge control storage tube comprising an evacuated envelope 10 having two neck portions respectively indicated as 12 and 14, symmetrically located about the axis of the tube. Within the envelope 'neck 12 is an electron gun 16 which may be considered as the viewing gun and which provides a conical spray of electrons. Within the neck 14 is a second electron gun structure 18 for providing a modulated beam of electrons which is focussed and deflected down the neck 14 into the envelope portion 10. Gun 18 is considered as the writing gun and is also used for erasing. Mounted at the large end of the envelope portion is a target assembly 20 comprising (a) a glass support sheet 22 having, on its surface facing the electron gun 16 and 1S, a thin iilm of transparent conductive material 24, which may be formed of metal or of a conductive compound such as tin chloride for example. On top of conductive lm 24, is formed a uorescent screen 26 which is of a phosphor material which will fluoresce under electron bombardment. Closely spaced from the surface of fluorescent screen 26, and at a distance in the order of several millimeters, is (b) a iine metal mesh storage screen 28, and (c) a second metal mesh screen 30 which is spaced beyond screen 28 at a distance in the order of 10 mm. Screen 3i) may be of a woven stainless steel mesh of A neness in the order of 230 mesh per inch, while screen 28 may be a metal screen having a neness in the order of 200 mesh per inch. Storage screen 28 is provided on the gun side with a coating 32 of dielectric insulating material, such as silica or magnesium uoride, and having a thickness in the order of several microns.

Screen 30 is mounted on a ring 21 of insulating material fixed within the tube envelope 10, adjacent to the tace plate 11 of the tube. Fixed to the insulating mounting ring 21 is an annular support ring 23, supporting, intermediate its ends, the glass target sheet 22. The ne metal mesh screen 28 is fixed across the open end of the metal support ring 23 which faces the electron guns 16 and 18. Screen 28 may be fastened. to support ring 23 in any manner such as by welding, for example. Also, mounted on the insulating mounting ring 21 is a sec ond annular metal support ring 25 across the open end of which is mounted a metal mesh screen 30 as shown in Figure l. The conductive target film 24 of the fluorescent screen is insulated from the metal support ring 23 by the glass support sheet 22. The conductive film 24 is connected as is shown by a lead 27 to a source of potential outside the tube envelope 10. Furthermore, the metal mesh screen 28 is provided with a potential during tube operation by connecting a lead 29 to the metal support ring 23, to which metal mesh 28 is attached. In a similar manner, metal mesh 30 is connected to a source of potential by a lead 31 attached to metal support ring 25 and to conductive coating 34. Normally theelectrodes 30 and 24 are maintained during tube operation at a constant potential. However, the metal mesh electrode 28, which is the storage screen, is connected, by means of lead 29, to a switch 33 which may be switched from ground to a source of potential as shown. Each of the metals of target assembly 2) is preferably made of some non-magnetic material such as some of the stain less steels or titanium.

The viewing gun 16 consists of a cathode electrode 7 having an electron emitting coating on its surface facing screen 20. A control electrode 13, and an accelerating electrode 15 are mounted successively along the axis of gun 16 Y` and between cathode 7 and screen 20. vThese electrodes arevmaintained, during tubeoperatiom at appropriate voltages to form the electron emission from cathode 1 into a wide beam or spray 44 of electrons. The

coating-i321'ofcolloidal graphite "adjacentfto Athe 'electron gun 16. yCoati-iigilfmay be Amaintained Aat'the samerp' tential asthe accelerating electrode-'15 of gun- 16, by means of lead-infn. f Y

"Electron gun-18, in like manner, consists ofl a-cath'ode electrode 19 Var`1`d`a-control grid-electrode 35 enclosing cathode `19. )Spaced along the gun axis toward 'the target are in order, 1a first, second, Iand'third accelerating-electrodes=37,f39,and 41respectively. Accelerating electrodes 37 'and `41are connected together as -shown land fto-ia source of. 'potential `whilel electrode 539 iis connected to a separate '.sourcelforifocussing. The 'wall vcoating 34E/extends .into' the' neck 114- ofthe writin'g'gun L18 and forms -a unipotential region `in which fthe electrons of '.gun 18 travel as aibeam 38 onto the target 20. Incoming signals may be applied .to the control lgrid 35 by any appropriate circuit means 43.

The voltages of thescvera1 electrodes disclosed in Figure 1 are illustrative of voltage values' which can be used duringoperation of the tube of the type described. However-,':these voltages are not limiting. 'Forexample, mesh grid 30 maybe operated Vbetween 200 volts and 2,000 volts :positive relative to ground. The conductive coating 24 may be operated within va range of 200 voltsto 2,000 voltspositive relative lto ground, while Lthe storage mesh k28 maybe varied between zero and a vminus '200 volts relative to ground. v

kAs shown in Figure 1, the metal mesh grid30 is operatedat around 1,'0O0Vvolts positive with respect to y.ground or `with respect tothe cathodepotential of the viewing gun V16. Also,vthe conductive coating 24 of the uorescent screen is operated at-close tor8,000 volts positive with respectto .ground Vor viewing gun cathode potential. `The potential of the metal mesh28, supporting the insulating coating32, is operated at arnegative voltage of 80lvolts, or atsground, which will `be explained hereinafter.

Surrounding the envelope adjacent the storage V,film 32 is a solenoid 36 that is energizedby a'direct current in the usual manner. Asis well known'the magnetic lines of force Aofsuch a coil-are curved and are` all perpendicularto the planesurface that isparallel to the Aplanes in which Vits coils are wound, and that is located-.on the effective center of its windings. e solenoid 36 is arranged'sothat this plane is the location of theestorage surface32.

The electron beam 38 from the writing gun 18 is scanned over the surface ,of the storage screen electrode 28 in Aany Well known marmer, as-for example, by two Y pairsof electrostatic deflection plates 40 and-42, respectively. 'As is well known, the pairs of vplates 40 and;42 may beeach connected to sources of saw-tooth voltages for providing line and frame scanning of the beamv over vthe surface of the mesh screen 28;

VReferring to Figure 3 thereis shown a vschematic diagramof the effect the y scfilenoid36 has on the viewing .and 'Writing'beams '38 and44 respectively. When the high vvelocityrbeams pass through theaperturedy electrode 30 V.they entera decelerating region Land are slowed down'to a few`volts velocity near electrode 32. Duetto this slow considerable time and thus the magnetic field of the solenid`36'is very effective Von the direction of the elec- Y' trons, and 'the electrons tend to follow theimagnetic lines of"force. VIt is folfthis reasonrthat the electronsof both Y the tube described Vand shown in Figure l, film 32 `fnaybe silica fand electrons striking a silica lm of this overpotential, will initiate a secondary emission greater than unity, i. e. the number of secondary electrons leaving any point of the dielectric surface 32 is greater than the number of electrons of beam 38 striking that point. Depending upon the potential Vat which screen 28 is set, electrons of beam 38 will .drive the insulating surface 32 to a uniform potential. A fraction of a second only is required to drive all of `thesurface to a uniform potential.

To prepare the target for storing a charge onrthe insulating coating 32, itV is necessary to establish a uniform potential over all of the lm 32. This is done by placing switch 33 Vto the -80 volt position and turning on the` writing gun 18. The electrons from the writing gunl 18 strike the insulator surface at a velocity ofV 20 volts, i. e.V

below first crossover potential, and drive all positive in-V sulator areas negative to the potential l(- volts)of the cathode 19. When this has been done,v switch33 is changedetothe` ground position and, due toi-the thinness ofthe insulating'ilm 32, ithe-viilm 132 is fcapacitively coupled to -th'ellba'clkplate potentialfsofthat film 132 follows the backplatefandtassurnesa potential `of -20 volts, i. e. the difference ofthe 1GO-.voltsv andV y-80 volts remains. Now when the viewingfbeami44 is turned on, theelectrons, which are' accelerated Lthrough the'spositive collector screen 30, zenter-v a retarding electric iield -adjacentthe surface lof lm 32-and are 'turned back'to'thecollector screen 30 vby the negative potential-of the film. When the -potential of insulating ilm132 -is 20 voltsvthe eld of '.lm 24 `does not penetrate-through 'the screen28 to attractfthe electrons tofthe uorescent screen vv26. This vis shown graphicallyby'Figure 2.

The beam 38 of lthezwritinggun is-then turned on again and ,scannedloverthe surface lof the insulatingv lm 32 while` being modulated .-by incoming signals, applied to the control ggrid 535 =by4 ithe: input -circuit 43. ATheV writing ibeam,;3'8strikes'fthe insulatingcoating ataenergies around '80;volts, which .is above 'theiirst `crossover-.potential fof theisecondary K emission curvey ofY the -silica rlm 32. .Inthisernannerrbeam 38Linitiates secondary, emission from .thefsilica "sur-facet -greaterpthan the number of electrons 4striking :the surface from i'beam .'38, :and .in ,those areas `where thebeam ,strikes,x;the.isilica surface'isdriven in a positivedirectiion .by'the .secondarygemission from its potential :of a 2O volts toward the viewing gun :cathode potentialrorground. lhe strength ofr'beam]4 38 determines the amount thatthe screen 28f'isgdriven :in

apositive directionV with -fulllbrightness occurring when i screen ,28 a is wat vground potential. VHowever, j no l, point of the surface'ofv film l32 canV 'be driven by'beam 38 rnorejpositive-.thanground,v sincefthe spray offelectrons 44 will land -on the 1m:atvthatpo'int .and drive it hack toygroundrpotent-ial or, .slightly below. zilnthose areas of thesilica film 32whichare drivenina positive direction Y toward ground `by beam 38,1thepositive'eld .of ,the iluorescent screen-2426` will now penetrate :andVV draw theflow velocity electrons vof, beam.44 through Lthe mesh .28.. VThese electrons of beam 4.4 which pass through mesh 28, fare highly accelerated by the intense positive eld betweenmesh: 28. and rtilm 24 .and will strike` the, fluorescent screen26- athigh velocities tocause luminescence of the screen. 'This l.luminescence will onlyV appear Vfrom portions lofsc'reen 261 adjacent those Vareas ofthe storage screen A*28 :struck kby "the writing 'beam'3'3. YWherel t 'bea1'n`38qdoes not strike `ilrn 3,2, vthe filmfrem-ainsnega-V tive' and 'the positive field o f 'thefluorescentscreenr can not penetrate,.through screen 28 Hto draw beam electrons 44 through to the iluorescent targetsurface A'This type lof writing, 'graphically represented in lFigure 2,l providesa picture .onthefuorescentscreen, which is I 'dark "in the'l unwritten lvareas and' light or 'bright in .the written areas. 4The.'backgroundiof the picture will -bev` black"an`d "the"writter1` areaswill .be white. vTheo- .retically,once avsignalhas, lbeenzwritten onthe .charge Storage.sc1:een.28,..ihmayV be `seen ,indeiinitely V4.on the n Y luminescent screen 26 since with the mode of tube operation as described above, the charged areas are never discharged -by the low velocity beam 44 because the lelectrons of spray 44 penetrate through the field of mesh 28. Actually, however, the stored charge on ilm 32 is gradually dissipated by spurious positive ions in the tube.

`In accordance with this invention, the stored signal on the insulating lm 32 may be selectively erased and the surface of the iilm rewritten on. Erasing may be done as described above by shifting the potential of mesh screen 28 in a negative direction, i. e. 8O volts, until the electrons of the writing beam 38 strike film 32 with energies below the rst crossover potential of the secondary emission curve of the insulating material. At this potential of electrode 28 any area of the surface of the insulating iilm 32 can be scanned by beam 38 and thus driven negative toward the potential of the writing gun cathode 19. Then, the screen 28 is reset to its ground potential and a new signal may be written down on the selected areas o-f the surface of the storage screen 32. Thus, any selected area may be erased by scanning this selected area with beam 38 when switch 33 is on the -80 volt position. Both the viewing gun electrons 44 and the writing gun beam 38 enter the target area perpendicular to the ilm 32 thus, the picture definition obtained is of an improved quality. 'The reason for this may be better understood by referring to Figure 3 wherein the beams are shown as arriving from exaggerated off-axis positions. Assuming that the target 32 has been written on Iby the writing beam 38 in such a manner that the insulator target 32 is -18 volts with respect to ground. It is obvious that electrons having such small energies could not be seen if the electrons 44 from the viewing gun 16 were arriving at lan angle. This is due to the fact that, with such low energies, if any of the component of the velocity is not along the tube axis the energies are not suliicient to go through the apertures in insulating film 32 and the electrons would return to the collector electrode 30. However, due to the effect of the magnetic lfield of solenoid 36 the electrons arrive perpendicular to target film 32 so that all of their energy is in a direction along the tube axis. Thus any electron from the viewing gun cathode 7, regardless of its angle of approach or location with respect to the target 28 arrives at the target assembly 20 as intended.

A further advantage .of the new and improved tube of this invention is that the writing beam 38 may now be used for selectively erasing any part of the stored information. In order to do this the writing beam 38 must land on the storage surface 32 at a velocity below Lfirst crossover potential in order to drive the storage surface negative below adjacent areas. Because of the fact that, without solenoid 36, some of the electrons of beam 38 would approach the target at different angles, not all of the surface would be driven to the writing gun cathode 19 potential and uniform erasure would not be possible. However, due to the field of solenoid 36, every electron that leaves the writing gun cathode 19 lands on the storage surface 32 below first crossover potential and perpendicularly thereto, thus providing uniform erasure in `any ofthe selected areas.

Although the invention has been disclosed in connection with specific details of preferred embodiments thereof, it must be understood that such details are not intended to lbe limitative of the invention except in so yfar as set forth in the accompanying claim.

I claim:

An electron discharge device comprising an elongated envelope, a target assembly in one end of said envelope, said target assembly comprising a substantially flat transparent support member having a transparent conductive coating on one surface thereof, a layer of phosphor material on said conductive coating, an apertured conductive mesh screen spaced closely adjacent to and substantially parallel with said phosphor material, an insulating coating mounted on the solid portions of said mesh screen and having apertures therein in registry with the apertures in said screen, an apertured collector electrode spaced closely adjacent to and substantially parallel with said insulating coating, `a iirst electron gun in the other end of said envelope for producing a low velocity electron beam directed toward said target assembly, a second electron gun in said other end of Asaid envelope for producing a stream of electrons directed toward said target assembly, a coil around said envelope and adja cent to said insulating coating 4for collimating said electron beam and said stream of electrons, said coil extending a substantially equal distance on each side of the plane of said insulating coating, whereby both said electron beam and said stream of electrons arrive at said plane in a path substantially perpendicular to said plane.

References Cited in the file of this patent UNITED STATES PATENTS 1 2,532,399 Schlesinger Dec. 5, 1950 2,547,638 Gardner Apr. 3, 1951 2,675,501 Friend Apr. 13, 1954 2,754,449 Farnsworth July 10, 1956 

